Analysis of HRT Heidelberg Retina Tomograph in High Myopic Patient

In high myopic patients with optic disc tilting, reference height is underestimated and many parameters depending on reference height will be changed with previous Heidelberg Retina Tomograph[HRT, under version 1.01].Therefore, care must be taken to classify the patients with tilted optic disc because underestimation of the amount of their cup area and volume may cause faulty decision to normal disc. However, by using "tilted analysis method" in recent HRT program[ver.2.01], we can expect to overcome such problems so, in this study we try to find out how much the HRT results are different between tilted and untilted analysis methods.We evaluated 26 high myopic patients under -6 diopters with tilted optic disc and glaucomatous visual field defects from March 1998 to July 1998. We compared their HRT parameters measured by untilted and then tilted method to each other.The mean reference height was changed from 0.2735 to 0.2892, the cup volume from 0.1961 to 0.1790 and the neural rim volume from 0.3060 to 0.3358 but glaucoma classification, the final conclusion of test, was not changed significantly due to neural rim volume and height variation contour increase with constant cup shape measure. Therefore, although refrence height is lowered and cup volume decreased with HRT[ver.1.01]in high myopic patients, if considering other many parameters, we can interpretate results rightly.

The Relationship between the Mean Height of Contour of the Retinal Surface at the Temporal Disc Margin and the Reference Height in Analyzing Optic Disc using Heidelberg Retina Tomograph

The relationship between the amount of posterior displacement of the retinal surface at the temporal disc margin and the reference height(HRef)in analyzing optic disc using Heidelberg Retina Tomograph(HRT;Heidelberg Engineering, Heidelberg, Germany)was evaluated. The displacement was measured as mean height of contour(MHC)in the temporal 40degrees C segment(20degrees C superior and 20degrees C inferior to the horizontal midline)of optic disc. HRef is a value representing the location of the standard reference plane. The accordances of HRef and stereometric parameters between right and left disc were also evaluated. MHC in the temporal 40 degrees C and nasal 40 degrees C segment, HRef, and stereometric parameters of optic disc were measured with the HRT in 244 eyes of 122 subjects. HRef was 0.376+/-0.099 mm in the right disc and 0.385+/-0.090 mm in the left disc. There was good correlation between HRef and MHC in the temporal 40degrees C segment(r=0.97, p<0.01), but poor in the nasal 40 degrees C segment(r=0.29, p<0.01). The accordances of HRef and stereometric parameters increased as the difference of MHC in the temporal 40degrees C segment between right and left disc decreased. HRef was affected by the amount of posterior displacement of the retinal surface at the temporal disc margin, which occurs in instances such as a tilted disc. We should find the method to adjust stereometric parameters to the amount of disc tilt.